This research summarized the basic concepts of compressed air energy storage(CAES)underground caverns from an engineering perspective, analyzed the basic structure of caverns and the main load characteristics of caverns during operation. On this basis, the basic design concept of flexible sealing structure was put forward, and the reliability design method was suggested to be adopted in the construction of underground caverns, which also provided the guidance and design principles, operation, and maintenance of CAES underground caverns.

Based on groundwater level data of 35 monitoring boreholes from 2015 to 2020 obtained from a large-scale underground water-sealed cavern project, the characteristics and causes of the changes in the groundwater level were systematically analyzed. Taking the construction progress of each cavern unit and geological structure information obtained from previous survey into account, those monitoring data revealed the influence of underground cavern excavation and artificial water curtain system on groundwater level, and the possible risk areas of low water pressure. According to the corresponding relationship between the temporal changes of groundwater level and construction progress, the monitoring boreholes could be divided into three types: water level maintains relatively stable,water level declines when adjacent tunnels were excavated; water level declines far after the adjacent tunnels were excavated. Combined with the spatial distribution of boreholes and the construction progress of underground caverns, it could be found that the groundwater level in the overall study area declined after the excavation of the underground caverns. However, benefited by the artificial water curtain, groundwater level in most area maintained higher than the safe water level(-25 m). Affected by faults F2, F3 and joint fracture zones L4, L8, local groundwater level in the southwest was still far below the safe water level(-25 m)at the end of monitoring, and it indicated a risk of insufficient water sealing. It indicated that the dynamics of the groundwater level in the study area was closely related to the construction progress and quality of the underground caverns, and the systematic monitoring of the groundwater level and timely analysis and feedback were essential. It is urgent to compile a specification for the underground water monitoring of the water-sealed cavern to promote more systematic monitoring of groundwater and improve the construction efficiency of the project.

The development history, cavern composition and role of underground compressed gas energy storage technology were systematically introduced, and the development status of underground lined cavern technology was discussed. This paper systematically analyzed the research progress of three key problems of underground lined caverns, namely ultimate storage pressure, thermodynamic effects in the process of gas injection and production, and sealing performance of cavern lining, summarized the existing research results, pointed out its limitations, and put forward suggestions for the future research direction of underground lined caverns.

Aiming at the water inrush disaster that was easy to occur during tunnel construction, the internal law of tunnel water inrush was analyzed through the statistics cases of tunnel water inrush. The water inflow in tunnels during construction was predicted by using the methods of long short-term memory neural network(LSTM), Elman neural network and multiple linear regression based on partial least square respectively, and compared with the actual water inflow, then the optimal method for predicting the tunnel water inflow was obtained. The results showed that water inrush accidents were more likely to occur in shallow-buried, long tunnels and extra-long tunnels, and in fault, karst and soluble rock strata. By comparing the prediction results of three different models with the water inflow during tunnel construction, the LSTM model had higher accuracy in predicting the water inflow in tunnels during construction.

In order to ensure the stability of the existing operation cavern, the blasting vibration analysis of the drilling and blasting excavation of the adjacent expansion cavern was carried out to clarify its influence on the stability of the existing operation cavern. Based on a domestic underground water-sealed cavern project, ANSYS/LS-DYNA was used to establish a three-dimensional numerical calculation model to carry out blasting vibration simulation, and its impact on the operating cavern was evaluated by peak vibration velocity and effective stress. The results showed that the vibration velocity of the monitoring point in the main cavern 1 was 0.1-0.8 cm/s, and the vibration velocity of the monitoring point in the main cavern 2 was 0.045-0.350 cm/s, and the maximum peak velocity appeared in the direction that was consistent with the propagation direction of the wave. The maximum single-stage explosive quantity affected the peak vibration velocity(combined velocity)and effective stress. The more the explosive quantity, the higher the vibration velocity and effective stress, peak vibration velocity could be increased by up to 200%. Under the condition that the maximum single-stage explosive quantity was less than 65 kg, the effective stress and the combined velocity at the nearest distance from the explosion source were less than the values specified in the safety regulations. The blasting construction of the expansion cavern had little impact on the operating cavern and had no potential safety hazard. Combined with the on-site blasting vibration monitoring data, the correctness of the simulation results was verified.

The paper reviewed the experimental research progress of prefabricated drilling and high stress real-time drilling in analyzing the mechanism of drilling pressure relief(DPR)for preventing rockburst disasters from the perspectives of macroscopic(mechanical behavior characteristics, failure characteristics, energy evolution)and microscopic(crack evolution), and elaborated on the rationality and effectiveness of DPR for preventing rockburst disasters. Theoretical research and experimental analysis had confirmed that DPR was a key technology for relieving high stress and high energy in deep surrounding rocks, providing a reference for optimizing the application of DPR to prevent rockburst. High stress real-time drilling test method was a more scientific new research method that revealed the internal mechanism of DPR to prevent rockburst. Based on this, six development directions had been proposed for the experimental research on the mechanism of rockburst induction and the current technical conditions of multifunctional testing systems to analyze the mechanism of DPR to prevent rockburst: developing high-stress drilling rig test equipment compatible with true triaxial test systems; considering disturbance factors in high-stress real-time DPR simulation tests; simulating real-time DPR test after excavation of deep tunnels(roadway)("3D six-sided loading-single-sided unloading-real-time DPR" test); constructing an analytical model for the energy evolution of surrounding rock under 3D high stress real-time DPR; exploring the relationship between the spatial size effect of pressure relief drilling and the stress field and internal energy dissipation mechanism of surrounding rock; establishing a computational model for rockburst prevention by DPR in large-scale high-stress surrounding rock based on numerical simulation software.

To study the performance of system combining common development and energy storage of deep geothermal energy under sustainable development conditions, seven evaluation criteria were defined. Thermal breakthrough time, water level and vertical displacement were used to assess the sustainable development of deep geothermal energy, and total recoverable energy, stored energy, energy gain coefficient and energy recovery efficiency were used to assess the operating performance of proposed system. Based on the well system which consists of two production wells and one injection well in Juancheng geothermal field, the coupled thermo-hydro-mechanical processes subject to seasonal exploitation and storage were demonstrated and the rationality and applicability of proposed evaluation criteria were validated, using the integrated geothermal reservoir model. The results showed that recoverable heat energy could increase about 360% by adding artificial thermal storage into common geothermal reservoir development, and the proposed system could meet the sustainable development demands of thermal breakthrough time, water level and vertical displacement. It is strongly recommended to add energy storage into the future geothermal reservoir development system, which promotes the development and utilization of urban deep geothermal energy on a larger scale and with higher quality.

In order to deeply understand the design principle and key technology of coal mine roadway oil storage and reconstruction project, the key technologies and engineering applications of coal mine roadway storage and reconstruction engineering were summarized through literature review and specific oil storage engineering cases.The site selection of the abandoned mine for oil storage should ensure that the crust of the mining area was stable, the geological structure was simple, the surrounding rock of the roadway was hard rock or relatively hard rock, the surrounding rock of the roadway was complete or relatively complete, the surrounding rock was weak in permeability and had a stable groundwater level. When the permeability of the surrounding rock of coal mine roadway was relatively discrete, and the water pressure of the surrounding rock was greater than the sum of oil and air pressure in the reservoir, it is necessary to reduce the permeability of the rock mass and carry out reconstruction by hydrodynamic containment method to realize the encapsulation of the roadway of the reservoir and control the leakage of oil products.When calculating the oil storage capacity of the coal mine roadway, it is necessary to consider the geological conditions of the roadway, the water curtain system, the corrective coefficient of the space occupied by the pump pit, the water bedding layer, and the blocking section of the oil storage reservoir, and also the oil supply volume transported from the nearby ports and wharves, so as to finalize the scale of the construction of the oil storage reservoir of coal mine roadway.

In order to explore the main influencing factors and control methods of secondary disasters of water and mud inrush in underground engineering, the prevention and control technology of secondary disasters of water and mud inrush was proposed by summarizing relevant cases since 2010 and the disaster-inducing environment and factors were summarized. Taking the secondary water and mud inrush of Shizishan Tunnel crossing F_Ⅲ-71 fault in central Yunnan as an example, the causes of disasters in this geological section were explored, and the evolution process of secondary disasters was divided into three stages: gestation stage, latent stage and induction stage. The methods of improving the state of the external environment, blocking the evolution path of the disaster and increasing the bearing capacity of the anti-outburst layer were put forward to prevent the recurrence of water outburst and mud outburst, which provided experience guidance for the treatment of the secondary disaster of water outburst and mud outburst.

Based on the theory of Darcy's law and solute transport, this paper took a groundwater-sealed oil depot project on a certain island as the engineering support and conducted numerical simulation research using COMSOL finite element software to analyze the variations in seepage field in caverns under different design schemes. The water-sealed safety of the cavern was evaluated. The development degree of seawater intrusion in the reservoir area was explored. The research indicated that the project required the installation of a horizontal water curtain, and the design pressure value of the horizontal water curtain should not be less than 0.2 MPa. The variation in the depth of the main cavern had a small impact on the water seal, and the recommended buried depth was -45 m. When the main carvern was fully excavated without oil storage, seawater would intrude into the caverns, with seawater intrusion showing a pattern of rapid intrusion followed by gradual intrusion, entering from the bottom of the main cavern.